Electronic devices, such as cellular telephones, must be supplied with power in order to operate. A detachable battery is used to supply power to the device, particularly when portability of the device is desired. The battery is secured to the device via a battery connector. The battery supplies power to the device until depletion occurs. Once depleted, the battery must be replaced or recharged if portable operation of the device is to continue. If no replacement battery is available and portability is not a concern, operation of the device may be continued by attaching an accessory to the device.
Accessories are attached to the device via an accessory connector of the device, such as the standardized eight pin J3-type accessory connector used in MicroTAC.TM. cellular telephones manufactured and sold by Motorola, Inc. from 1989 to the present. The J3-type accessory connector has an external power supply pin; an audio in pin; an audio out pin; data pins for high speed data communications according to the three-wire bus protocol used in radiotelephone products by Motorola, Inc.; and two grounding pins in a predetermined arrangement. To be compatible with the J3-type accessory connector, an accessory must have a connector that is designed to mate with the accessory connector and have the same number and arrangement of pins. Upon attachment of the accessory to the device, the battery is electrically disconnected by an internal switch arrangement employed by the device and the device is powered solely by the accessory, which couples power transformed from an automobile electrical system or a conventional wall socket to the external power supply pin.
Unfortunately, because the battery is disconnected upon attachment of the accessory, charging of the battery can not be accomplished via the accessory connector as described. In the past, charging of the battery was performed by detaching the battery from the battery connector of the device and placing it in a standalone charger or by providing a dedicated charger connector on the device separate from, and in addition to, the accessory connector and the battery connector that fed a current source circuit disposed in the device. The standalone charger lacked portability, while the dedicated charger connector and current source circuit added cost and complexity to the device. Therefore, what is needed is a low cost apparatus and method that permits charging of the battery by the device and maintains backward compatibility with past accessories that mate with the accessory connector of the device.